I don't know how much I trust a general Google search with stuff like this but, for what it's worth, this description seems to fit my gun exactly:
A Springfield Armory M1911-A1 with a 5-digit serial number prefixed by "NM" generally dates from the mid-1980s to early 1990s.
These early...
Hi all (I just joined the Forum)
I just came home with this awesome old Springfield Armory M1911-A1 Cal .45 (so cool!)
I'm pretty sure it's from the late 1980s (see below), but I'm having trouble pinning down the exact year of manufacture (serial Number NM42905). I'm gonna call Springfield...